5 - Mitochondria and Oxidative Phosphorylation Flashcards
What is the theory of endosymbiosis? and why does this explain mitochondria having their own DNA
- Ancestral eukaryotic cell engulfed an aerobic bacterium (mitochondria) by endocytosis
- The cell could provide the bacterium with resources and the bacterium could provide the cell energy from oxygen
- forming a symbiotic relationship
- As a result mitochondria have their own genome and biosynthetic machinery for making RNA and Proteins
Describe the mitochondrial genome
- Singular circular chromosome
- Located in the matrix
- 37 genes in total: 2 rRNA, 22tRNA, 13 protein encoding
- very small compared to nuclear genome
what happens to male mitochondrial DNA?
- It is degraded as soon as the sperm fertilises the egg, so we only have maternal Mitochondrial DNA
Talk about mitochondrial fission and fusion
- Mitochondria are constantly fusing and dividing
- if for example 2 mitochondria fuse, then 1 large mitochondria will have 3 copies of mtDNA
how does mtDNA replicate
- randomly
- just before fission mtDNA localise to mitochondrial polarities, to ensure they are incorporated into the new one
definition of Mitochondrial Biogenesis
the increase in abundance of mt proteins, mtDNA and mitochondrial numbers
when does mitochondrial biogenesis occur
when cells are stressed and need to produce more ATP
- eg during exercise
Describe the mitochondrial ribosome and the link to the mitochondrial genome
- There are 2 rRNA genes in the mitochnodrial genome
- rRNA form the subunits of ribosomes
- Large 39s subunit made of 50 proteins
- Small 28s subunit made of 30 proteins
- Overall 55s and 80 proteins
what does s indicate
- how fast they fall in a tube of suspension
55s mitochondrial ribosomes synthesise proteins coded by mtDNA, but mitochondria need more proteins than they can make to survive, where do these proteins come from
- cytosolic/cytoplasmic Ribosomes
is the inner mitochondrial membrane very permeable or impermeable
- inner is very impermeable
- outer is more permeable
Describe how precursor proteins in the cytoplasm enter the mitochondrial matrix
- chaperone proteins bind to the precursor protein and prevent it from folding so it can be pulled into the matrix
- The special signal sequence on the precursor protein binds to a receptor protein in TOM complex on outer mt membrane
- TOM pulls the protein across the outer membrane into the intermembrane space
- The special signal sequence then binds to TIM 23 complex which translocates the precursor protein across the inner membrane
- the chaperone protein is then lost and the special signal sequence cleaved leaving the protein to fold
what enzyme cuts off the special signal sequence from the precursor protein
- signal peptidase
What do TOM and TIM stands for and where are they located
TOM - Translocase Outer-Membrane complex
Tim - Translocase Inner Membrane complex
What is a special signal sequence
- a specific series of amino acids recognised by a specific receptor
How does Pyruvate transport into the mitochondrial matrix from the cytoplasm
- Pyruvate is small enough to travel through porins in the outer mitochondrial membrane
- Pyruvate then travels from the intermembrane space into the matrix through Mitochondrial Pyruvate Carriers
what happens to pyruvate once its in the matrix
- pyruvate is decarboxylated to form Acetyl CoA
How do Fatty acids transport into the Mitochondrial Matrix
- Fatty acids cannot cross either mt membrane so have to be converted
1) Fatty acid is combined with CoA forming fatty Acyl CoA in an unfavourable reaction costing 1 ATP
2) fatty Acyl CoA is then combined with carnitine via the enzyme CPT1 located on the outer mt membrane, this forms Acyl-Carnitine
3) Acyl-Carnitine can travel through porins through the outer mt membrane
4) Acyl-Carnitine is then transported into the matrix through the protein translocase which is an antiporter which moves carnitine out of the matrix at the same time
What happens to Acyl-Carnatine once it is in the matrix
Acyl-Carnitine in converted back into fatty Acyl CoA and carnitine by CPT 2, Carnitine is then shipped out of the matrix through the protein translocase antiporter
Where are CPT1, CPT2, porins and protein translocase located?
CPT1 and Porins - Outer mitochondrial membrane
CPT 2 and Protein translocase - Inner mt membrane
What do the proteins CPT1, CPT2, porins and protein translocase do or transport?
CPT1 : Combines fatty acyl CoA and Carnitine to produce Acyl-Carnitine
CPT2: Converts Acyl-Carnitine back into fatty acyl CoA and Carnitine
porins: Acyl Carnitine
protein translocase: Acyl carnitine
How is NADH transported into the the mitochondria
The Malate-Aspartate shuttle
- Oxaloacetate in the intermembrane space is reduced to malate through the oxidation of NADH
- Malate can travel into the matrix through an antiporter protein with a-ketoglutarate
- Malate is now oxidised into oxaloacetate again, which in return reduces NAD+ into an NADH
- Oxaloacetate is transaminated into aspartate, while glutamate is converted into a-ketoglutarate
- Aspartate can travel back into the intermembrane space through an antiporter when glutamate enters the matrix
- Aspartate is then transaminated back into oxaloacetate and a-ketoglutarate is converted into glutamate
what enzyme catalyses transamination of oxaloacetate and aspartate
- transaminase
where does the malate aspartate shuttle occur
across the inner mitochondrial membrane
what enzyme catalyses the reduction and oxidation of malate and oxaloacetate thus reducing and oxidising NADH/NAD+
Malate dehydrogenase
where is oxaloacetate reduced
when oxaloacetate is reduced, NADH is oxidised into NAD+, which reduces the amount NADH. we want more NADH in the matrix so this happens in the inter membrane space
Name all the proteins we know on the inner mitochondrial membrane
- TIM (Proteins transport)
- Mitochondrial pyruvate carriers (pyruvate transport)
- Acyl-Carnitine translocase (Fatty acid transport)
- Antiporters in malate aspartate shuttle (NADH)
Name all the proteins we know on the outer mitochondrial membrane:
- TOM (protein transport)
- Porins (pyruvate and fatty acid transport)
Name the complexes in the electron transport chain
1- NADH dehydrogenase
2- Succinate dehydrogenase
3- Cytochrome C reductase
3- Cytochrome C oxidase
what are ubiquinone and cytochrome
- mobile electron carriers
give a summary of the electron transport chain
- high energy electrons carries by NADH and FADH2 are passed into the electron transport chain and accepted by a series of electron carriers
- The electrons lose their energy as they pass along the chain
- the energy pumps H+ across the inner mitochondrial membrane to the intermembrane space
- the electrons are passed to oxygen forming water
Describe the structure of complex 1 in the ETC
- FMN is the electron acceptor
- There is an iron-sulphur cluster that links FMN to ubiquinone (Q)
Describe the process of what happens at Complex 1
- NADH donates is electron to complex 1 (NADH dehydrogenase) and is oxidised to NAD+
- FMN accepts the electron and passes the electron down the series of iron-sulphur clusters to ubiquinone
- Ubiquinone (Q) accepts the electron forming QH2 or CoQH2, now having the energy from the electron
- In passing the electrons down the iron sulphur clusters some electron energy some electron energy is lost and used to pump 4H+ across the inner mt membrane into the inter-membrane space
What are the results of complex 1 NADH dehydrogenase
- 4 H+ pumped into the inter-membrane space
- an oxidised NADH or (NAD+)
- ubiquinone with an electron (CoQH2 or QH2)
Describe the process of what happens at complex 2 (succinate dehydrogenase) in the electron transport chain
- At complex 2 succinate is oxidised into fumarate (step 6 of the TCA cycle)
- At the same time FAD is reduced into FADH2
- FADH2 instantly donates its electrons to complex 2
- The electrons pass down a series of iron-sulphur clusters until reaching the final stop
- at the final stop CoQ is reduced to CoQH2 by gaining 2 electrons and 2 H+
what is the final result from complex 2 in the electron transport chain
- Succinate is oxidised to fumarate
- FAD is reduced to FADH2
- CoQ is reduced to CoQH2
describe the process of what happens at complex 3 (Cytochrome C reductase) in the electron transport chain
- CoQH2 from complex 1 or 2 donates its 2 electrons to the iron-sulphur clusters in complex 3 becoming CoQ
- The 2 H+ from oxidised CoQH2 are released into the intermembrane space
- The electrons pass across the iron-sulphur clusters to cytochromes.
- Cytochromes accept the electrons and pass each one to a cytochrome C mobile electron carrier
- Enough energy is released by the electrons in the iron-sulphur clusters to pump 2 more H+ into the intermembrane space
What is the result of Complex 3
- CoQH2 is oxidised donating 2 electrons to complex 2 and also 2 H+ are released into the intermembrane space
- 2 H+ are pumped into the intermembrane space
- 2x Cytochrome C mobile electron carrier gains an electron and is reduced
Describe the structure of complex 3
- Contains a series of iron-sulphur clusters which lead to cytochrome
- also has cytochrome C which are mobile electron carriers attached
Describe the process of what happens at Complex 4 (Cytochrome C oxidase) in the electron transport chain
- 4 cytochrome C mobile electron carriers arrive and donate their single electrons to complex 4
- This has to be 2 electrons generated from 2 FADH2 (Complex 2) and 2 NADH (complex 1)
- These electrons are passed to an O2 molecule and combines with 4H+ from the matrix to give 2 H20
- This combination generates enough energy to pump 4 H+ from the matrix into the inter membrane space
What is the result from complex 4 (Cytochrome C Oxidase) in the ETC?
- 4H+ pumped into intermembrane space
- 2 H2O generated
- 4 Cytochrome C oxidised
What are the 3 driving forces that result in oxidative phosphorylation
- Large pH difference
- Large concentration gradient
- Large electrical charge difference
Describe how ATP synthase uses the electrochemical proton gradient to generate ATP
- Protons enter ATP synthase through the F0 region into the a subunit
- Protons then move into the c subunit of the F0 region causing some rotation/mechanical energy
- The protos leave into the matrix after driving around the c subuint
- c is linked to the shaft which rotates very quickly
- as the shaft rotates this causes a conformation change to alpha and beta subunits of F1 which catalyses the formation of ATP
Describe the structure of ATP synthase
- 2 regions F0 andF1
- electrons enter and pass through F0
- F1 is where ATP is generated
- F0 contains subunits abc
- F1 contains subunits alpha and beta
